In general, resolvers, sometimes referred to as "rotary inductors", are used to provide output electrical signals which vary as a function of the angular displacement of a rotating shaft and normally comprise a stator and a rotor member, most often formed of laminated high permeability magnetic material. The stator member has one or more active stator primary coils and the rotor has one or more active rotor secondary coils, the magnetic coupling between the stator and rotor coils being varied by rotation of a shaft on which the rotor is mounted. Such devices thereby transmit electrical information concerning the angular shaft position. By changing the relative orientations of the primary and secondary windings, by rotation of the rotor shaft and thereby varying the magnetic coupling therebetween, the output voltages from the rotor secondary windings are a measurement of the shaft's rotating position. Since the rotor is generally free to rotate continuously, the connections to the leads thereof have to be implemented by the use of conventional slip rings and brushes.
Such resolvers are generally considered as precision devices and in many applications require extensive fabrication and alignment procedures and compensating circuits so that the desired precision can be achieved and maintained in operation. The cost thereof can be considerable, particularly in such devices as used to sophisticated applications requiring an extremely high degree of precision.
In many other applications, however, where extremely high precision measurements are not absolutely necessary or even where high accuracy is required, it would be desirable to utilize a resolver which is much less expensive to fabricate but which has sufficient precision to provide the operation desired. In addition, in many applicatios it is often desirable to provide more than one speed of operation, i.e., where one rotor revolution provides a plurality of voltage output cycles, using the same stator/rotor combination and it is desirable to do so in a relative simple and inexpensive manner.